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Brake help needed?
Hi all,
Those that know me will remember I posted about binding rear brakes about a year ago! Anyway I still have this problem and have covered 1300 miles! I am onto my second set of rear discs and second set of rear pads. Most of the time the rears are on about 40% and the fronts I don't have a problem with. I have to date changed all my stainless lines,unions had them pressure bled at a garage and today removed the bias valve to see if that was the problem with no effect? This is now about to tip me over the edge! In a nut shell.....both rear calipers have full travel and work really well for the first 6-8 mins of driving and are free! After that time when brakes have been used a bit they bind on?? Both by exactly the same amount Any advice or help please as I am contemplating taking a hammer to the whole car! Cheers Craig |
Hi Craig.
Are there the standard Rover 200/400 rear claipers? If so, I know the Rover guys have quite a few problems with them seizing/sticking the same as you. Only thing I can suggest is try a new set of calipers (possibly recon ones) or recon yours. Theres a really good tutorial here: http://www.rovertech.net/forum/viewt...hp?f=6&t=50092 If you can't read it or not a member, I can try and paste the contects here. |
Sounds like either a caliper issue or possibly a handbrake issue. thats exhibiting itself when the brakes heat up. I would tend to err to the latter as it sounds like its effecting both sides equally and you'd be extremely unlucky to get 2 calipers stick at the same time.
Can understand its gonna be a right pain to identify though if it only happens when run for a few miles. I suppose the only other thing (really remote) it could be is the master cylinder as I beleive they normally apply the back before the front so if the pedal isnt returning fully then it would be the back that has some pressure first. Understand the feeling of :frusty: the brakes at the moment are the one bit my car seems fine on although not driven it yet to see. Getting a mating that I'm happy with between teh column and the steering rack and the sorting the clutch out have been long and still on-going jobs. Have finally resorted to booking it in for a bit of TLC with Talon sportcars to sort those two jobs out so I can move on in the build. |
Cheers for the quick reply's guys!
I probably should have put in my initial thread I know it's not a handbrake issue as the release mech works fine (already checked) and I have no preload on the master with full pedal travel. I thought the preload was the problem ages ago as it seemed to go away when altered but this was not to be! So the only parts I have left to change are the master cylinder and rear calipers which have full piston travel and brand new sliders!! However after reading some of the rover stuff it seems the sliders can sieze after no time at all and although mine has not done many miles it has been stood for nearly 2 years so I will have a look at these again! I will let you know what I find Ps I forgot to say that when the rears start to bind the brake pedal becomes extremly hard? would this happen if it was sticky calipers? Craig |
This is the sticky from Rovertech. You may know most of this Craig, but an interesting read on how they do it anyway.
For some reason, 200s, 400s and coupes suffer badly from sticking rear calipers. This leads to poor handbrake effort, overheating brakes and the need to replace the pads every 4 months. For the relative noob this can be quite a daunting job but it really isn't that hard and to show it I have compiled this little tutorial. Hope it is useful. Due to the extreme heat a sticking caliper produces you might see something like this http://img.photobucket.com/albums/v3...g/1b745f0e.jpg Put the car into 1st gear and leave the handbrake off. Chock the wheels and crack the wheelnuts. Jack the corner of the car up and support the car on axle stands. Next remove the two 8mm bolts holding the dust cover. Remove the two 12mm caliper retaining bolts. http://img.photobucket.com/albums/v3...g/9d4ee615.jpg Note the copper grease on the threads. As this area is exposed to heat I always reassemble with copper grease to protect the threads and to prevent seizing. http://img.photobucket.com/albums/v3...g/171ee20b.jpg Lever the caliper away from the carrier as below. http://img.photobucket.com/albums/v3...g/da211b93.jpg These pads have covered less than 3000 miles http://img.photobucket.com/albums/v3...g/69fab9a9.jpg It is important to find an appropriate tool for this next job. It must be a lever with a flat edge as it is used to wind the piston in and out. I use a steel chisel. Place the lever in the groves in the piston and turn the piston anti clockwise until it just turns without coming out anyfurther. Unwinding the piston can be easier said than done as they can be quite tight. http://img.photobucket.com/albums/v3...g/2cb48d18.jpg To fully remove the piston just press the brake pedal a couple of times. Go back to the piston and pull the piston free from the seal. NOTE, the piston will need cleaning hence why I remove it. You can leave it in but I recommend removing it to give it a good scrub with a scourer. You can see why this caliper was seized. http://img.photobucket.com/albums/v3...g/1aaba586.jpg After a bit of scrubbing with a scouring pad and brake cleaner this is how it looks. There is some minor pitting but nothing to worry about. http://img.photobucket.com/albums/v3...g/a733826c.jpg The next bit can be a bit tricky but comes with experience. You need to pul the boot over the base of the piston. I find the best method is to hold the boot over one edge of the piston with one finger and then run a small screwdriver under the seal to pull it over. http://img.photobucket.com/albums/v3...g/7ef35512.jpg Apply pressure to the piston while winding it in clockwise. When it bites and starts winding in apply some copper grease around the ridge as so. http://img.photobucket.com/albums/v3...g/1a0f73ee.jpg Wind the caliper all the way in. It will keep turning when it is all the way in too. I like to apply copper grease to the piston face and seal to try and prevent future water ingress. http://img.photobucket.com/albums/v3...g/91308c82.jpg Next lever off the slides. http://img.photobucket.com/albums/v3...g/41e8ef18.jpg http://img.photobucket.com/albums/v3...g/c799ab20.jpg Clean them up with a sharp implement as there is usually corrosion and a build up of crap on them. Failure to clean the slides will lead to the pads sticking. Loverly! http://img.photobucket.com/albums/v3...g/653b3e21.jpg Put the new pads in with plenty of copper grease on the back of the pads. http://img.photobucket.com/albums/v3...g/068fb390.jpg Reassemble the caliper and dust cover. http://img.photobucket.com/albums/v3...g/aa137bb3.jpg Using an 11mm ring spanner, undo the bleed nipple and ask a helper to press the brake pedal until you get clean brake fluid with no bubbles in. Once you have clean fluid coming through, nip the bleed nipple up during the down stroke to stop any air getting back into the system. Put the wheel back on and go for a rag. Remember to pump the pedal before you drive off. |
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I have 2 brand new calipers knocking around if you want them.
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Chris,
Yes I have a spring return but tried lifting pedal and removing all pressure to no avail. John d, Mine are the 160 rears! Is that what you have spare? If so what do you want for them? John, I took of the rear nearside piston today and it was (as new) with no rust or wear but getting the boot back on was a nightmare and eventually it split. lol |
Hi Craig,
I have no experience of Rovers but sounds like the master cylinder not releasing the pressue in the lines when you release the brake pedal. Is there anything stopping the master brake cylinder returning completey? Also, read this tutorial... http://books.google.com/books?id=5rW...age&q=&f=false Is your master cylinder from a car with rear drums as these have a residaul pressure valve, but you've probably checked that already. good luck, ...peter |
240mm calipers, so no use.
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Hi peter,
The master cylinder is from an elise/exige so discs all round. The pressure build up is what is playing on my mind! As when the brakes bind the brake pedal gets hidiously hard and I may be wrong but I don't think this would happen if it were just the rear calipers binding |
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I had a similar occuance of the brakes binding on and the pedal being really hard many years ago on a Spartan Treka. One telling thing was when releasing a bleed nipple I got a brief squirt of brake fluid, indicating it was caused by hydraulic and not mechanical reasons.
In my case I had a small leak from the master cylinder that was stopping the piston returning fully. After a few minutes the leak would drain into the servo and the pedal work again. Just a thought. |
I hope i am not repeating something you may have already been told but have seen similar to this before. the cause was to much preload on the master cylinder from the brake servo. This was cured by removing the master cylinder from front of the servo, the rod that sticks out the end of the servo and protrudes into the master cylinder was slightly too long ( gives a very high brake pedal especially when brakes hot). on some cars there is an adjuster on the end of this rod which can be screwed in and out, adjusting the preload on the system. have not removed the master cylinder on my own 5exi to check if this is present on my servo but if not present in your own then the preload could be adjusted by removing small amount of metal from end of rod with a file or placing a couple of thin washers on the master cylinder mounting bolts before refitting the cylinder to the servo. As these are safety critical items you are dealing with please recheck operation before driving.
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Any luck fixing this yet Craig? I mentioned the problem to a friend of mine and he mentioned he'd seen a car with similar problems that turned out in the end to be that the brake light switch was mounted too close to the pedal and was preventing it fully returning, leading to the pressure build up. I guess whatever the cause, all these kind of problems would be diagnosed by finding that the clevis pin isn't free to wobble in the pedal when fully returned.
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Yup this is the reason why I know it's nothing to do with pre-load, brake switch etc as the clevis has always been free to wobble on brake pedal return and if I tap the brake pedal sharply and release with my foot I can hear the clevis slap of the piston. Anyway no luck sorting yet as I wrecked the piston seal trying to put it back on and with no rear suspension have not done much! |
Craig i am afraid the theory about a slack clevis only applies to a straight master cylinder not a servo. the rod with clevis you refer to only reaches as far as the back of the servo and is held by a circlip. the rod protruding from the front of servo into your master cylinder is part of the servo mechanism and has its own back stop. to take up differences in tollerances that fron rod is normally adjusted at factory to take account of the clerarances no the master cylinder fitted to the servo. if yopu have a very hard brake pedal which gets worse on driving still suspect the preload. this can be double checked if your brakes lock up by opening a bleed valve, the brakes will release .
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To clarify, and avoid confusion, there's no servo on Craig's car, just an S1 Elise master cylinder.
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Just seen this on the Merlin Motorsport website...........
THE LEARNING CURVE This problem came from a very competent builder of specialised 4X4 vehicles. He was using Girling master cylinders. The problem was that after applying the brakes one circuit retained the pressure and would not release. Opening the bleed valve released the pressure; the brakes could then be applied but would again not release the pressure. We had seen this problem before. It is caused when the brake pedal hits a stop and does not allow the push rod to retract fully. This means that the piston in the master cylinder does not uncover the port and allow the pressure in the system to release. The solution is to make sure that when the pedal is released there is a small amount of play in the push rod. The customer was adamant that the pedal was releasing fully but still the brakes would not release. He returned a week later to explain what had happened. The analysis was correct but for a different reason. He had changed the push rod and when replacing the washer and circlip he had fitted the washer the wrong way round. The washer is about 3mm thick with a chamfer on one side to accommodate the ball on the pushrod. The chamfer should be on the inside which allows the ball to fit in the chamfer. The other way round stops the piston from retracting fully. |
Peter,
Thanks for that very worthwhile....but unfortunetly mine does not have any washers holding in the pushrod....simple knuckle and ball and the only thing stopping the pushrod just falling out is the fact it is connected to the pedal! Craig ps I still think that the master is to blame though |
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